| NOx is one of the global atmospheric pollutants, selective catalytic reduction of flue gas denitrification technology is an effective method to remove fixed or mobile sources of NOx. In recent years, low-temperature SCR technology had been attracted more and more interests around the world for its simple structure, high denitration efficiency, reliable operation, easy maintenance, etc. While according to the review of the current research of SCR technology,the following shortcomings were bottlenecks of achieving large-scale industrialization: low catalyst activity at low temperature, uncertainty of the kinetic reaction and SO2-poisoning mechanism. Therefore, the kinetics and SO2-poisoning mechanism on supported catalyst were systematically investigated in this dissertation.V-W-Mn-Cu-Ce/TiO2 was prepared with impregnation method, using TiO2 as the carrier.The effects of temperature, O2 concentration and [NH3]/[NO] molar ratio on SCR activity of catalyst were discussed respectively. The results showed that activity was enhanced with temperature increasing, then stayed around 95% at above 350 ?. When [NH3]/[NO]<1.1, the NO conversion increases by temperature increasing; when [NH3]/[NO]?1.1, activity remained unchanged. When concentration of O2 blow 4%, the denitration activity increased with the concentration increasing, When O2?4%, NO conversion was stable. Intrinsic kinetic parameters and the corresponding kinetic equation of catalysts were calculated by empirical way. Based on transient response technology, NH3-SCR reaction on the catalyst V-W-Mn-Cu-Ce/TiO2 mainly took place between strong adsorbed NH3 species and gas-phase or weak adsorbed NO (complied with Eley-Rideal mechanism).Mn-Ce/TiO2, Cu-Ce/TiO2 and Mn-Cu-Ce/TiO2 was prepared with the same method.According to the activity, the order of kinetic parameters Ea and A size were calculated:Mn(0.2)-Ce/TiO2> Mn(0.5)-Ce/TiO2> Mn(0.4)-Ce/TiO2> Mn(0.3)-Ce/TiO2; Cu(0.1)-Ce/TiO2> Cu(0.4)-Ce/TiO2 > Cu(0.3)-Ce/TiO2 > Cu(0.2)-Ce/TiO2; Mn(0.2)-Cu(0.2)-Ce/TiO2 >Mn(0.1)-Cu(0.3)-Ce/TiO2> Mn(0.3)-Cu(0.1)-Ce/TiO2. The relationship between the catalysts'surface properties and denitration performance were compared and analyzed through XRD,NH3-TPD and TPR.Furthermore, the effects (Denitration activity within 4 hours decreased from 85% to 50%less) and reasons (Deposited of the metal sulfate salts and ammonium sulfate on the surface)of SO2 on the catalyst V-W-Mn-Cu-Ce/TiO2 were examined and analyzed. Meanwhile, five factors about SO2-poisoning,including the adsorption of SO2, the adsorptive conversion,H2O,temperature and catalyst components were discussed. The results showed that SO2 adsorption on the four kinds of catalysts' surface were in different degrees. Multi-component catalysts were more easily to be absorbed SO2 and the amount of the generated compound was larger.V-W-Mn-Cu-Ce/TiO2 has a low SO2-absorption conversion rate at low temperature. The active ingredient Mn could be effectively reduced SO2-absorption conversion in the range of 200 to 350 ?. H2O would lead to the increasing of the mount of toxic substances' production on catalyst surface,the order was: Cu-Ce/TiO2 > Mn-Cu-Ce/TiO2 > Mn-Ce/TiO2 >V-W-Mn-Cu-Ce/TiO2. Increasing reaction temperature could reduce the number of deposit sediment on catalyst Mn(0.2)-Ce/TiO2. Under the conditions of 180?, Mn-Cu-Ce/TiO2 was more easily poisoned than Mn-Ce/TiO2 and Cu-Ce/TiO2 during SCR reaction with SO2, and then deactivated.Finally, metal sulfate salts' and ammonium bisulfate's thermal stability were studied and their impact on the different components of catalyst's SO2-poisoning were researched either.The mechanism of catalyst's SO2-poisoning during SCR reaction was explored. Through TG-DTG and FT-IR, thermal stability of ammonium sulfate salt on Mn-Ce/TiO2 was worse than that on Cu-Ce/TiO2, while on Cu-Ce/TiO2 thermal stability of metal sulfate was worse.With being compared, there was a greater impact of the thermal stability of salt on multi-component catalyst. The reason why catalyst deactivated at the sulf-atmosphere was that metal sulfates and salts of ammonium sulfate were deposited on the catalyst surface with different components during SCR reaction, which the catalysts were poisoned. Ce doping and changing reaction temperature could improve catalysts' the degree of SO2-poisoning. |
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